A typical frame transfer charge coupled device ("frame transfer CCD") comprises a vertically-oriented, oxide-covered silicon substrate upon which an array of horizontally-oriented, semi-transparent electrodes (e.g., polycrystalline silicon) are mounted. Vertically-oriented charge transfer channels within the substrate and beneath the horizontally-oriented electrodes are defined by electrically inactive p-type "channel-stop" regions. The horizontally-oriented electrodes are grouped into an upper "image zone" and a lower "memory zone". An array of vertically-oriented electrodes are also mounted on the substrate, and a horizontally-oriented charge transfer channel is provided thereunder within the substrate, to define a horizontal serial shift register adjacent to and below the memory zone. The serial shift register receives charges line-by-line from the vertical charge transfer channels, and provides a corresponding video signal to a charge detection amplifier mounted on the substrate. The amplifier transmits the video signal to an output.
When frame transfer CCDs are used in a normal staring mode, an optical image is focused upon the image zone, and due to resultant photon penetration through the electrodes and the electrical biasing of electrodes, charges are built-up, or integrated, over discrete time periods in "potential wells" within vertical charge transfer channel regions beneath biased electrodes. Such integrated charges, or frames, which are representative of the image, are then rapidly transferred by "charge coupling" to the memory zone. Charge coupling occurs by electrically and sequentially pulsing adjacent electrodes or sets thereof to establish differentials therebetween. Frames of charges held in the memory zone are then transferred line-by-line by charge coupling into the serial shift register, and each line is shifted out sequentially to the charge detection amplifier. The signal provided by the serial shift register is typically in a television-compatible format.
As will be appreciated by those skilled in the art, a memory zone has generally been employed to hold charges as a queue to the serial shift register. As such, it is readily understood that known memory zones are covered by continuous opaque shields to preclude receipt of radiation, thereby preserving the integrity of the charges stored thereby.
Levine's U.S. Pat. No. 3,931,463 discloses an apparatus for achieving image brightness control in a frame transfer CCD. As is conventional, the Levine device includes an image zone, a memory zone and a shift register having a number of stages equal to the number of charge transfer channels employed. A drain diffusion is provided at the image zone end of the charge transfer channels for receiving undesired charges from potential wells. By appropriate backward pulsing of the electrodes within the image zone, undesired charges in the image zone can be selectively "reversed clocked" to the drain diffusion. In the Levine system, effective noise resulting from feedthrough during charge transfer to the drain diffusion is reduced by performing the process during horizontal retrace periods of standard televisions.
For some applications, the horizontal retrace period is not long enough to allow all unwanted charge in the image zone to be drained. To overcome this problem, Bell, et al. U.S. Pat. No. 4,651,215, have proposed the use of a frame transfer CCD employing backward shifting of charge to a diffusion drain during active transmission periods. The Bell, et al. device includes means for applying reverse clocking pulses just before the start of integration periods at a frequency outside the output signal bandwidth.
In the Hashimoto, et al. frame transfer CCD device disclosed in U.S. Pat. No. 4,689,686, charges generated in at least a portion of the image zone are transferred down to the shift register for read-out at a high speed, at predetermined intervals, so that image data regarding photometering or distance metering or the like can be selectively obtained at high speed. This permits control operations for photometering or distance metering to be executed at a high speed. Hashimoto et al. contemplate use of an iris in connection with the image zone to control the amount of image radiation received in connection with the disclosed device.
The method of Roy, et al., disclosed in U.S. Pat. No. 4,644,405 is directed to selectively transferring image data received within a selected portion of an image zone to a memory zone for processing. By utilizing a selected portion in the image zone, Roy, et al. considerably reduce the time associated with transmitting corresponding charge from the CCD for processing.
Although the above-noted patents represent advances in the field of electronic image receipt and transmission, they do not specifically contemplate selective, alternate use of the corresponding disclosed CCD devices for normal staring array imaging and for scanning, or rotating, a CCD face across a wide field of interest, i.e., "wide sector searching". More particularly, such patents fail to disclose apparatus which are capable of operating in dual modes for normal staring array imaging and wide sector searching, while minimizing componentry, space and cost requirements, as well as operational problems.